Thermal blanket circulating and control means



Dec. 23, 1958 E. M. SMITH 2,866,072

THERMAL BLANKETCIRCULATING AND CONTROL MEANS Filed .Jan. 9, 1957 2Sheets-Sheet 1 INVENTOR. EDWARD M. SMITH Dec. 23, 1958 E. M. SMITH2,866,072

THERMAL BLANKET cmcuuwmc AND CONTROL MEANS Filed Jan. 9, 1957 2Sheets-Sheet 2 INVENTOR. EDWARD M. SMITH A Tram/5r V United StatesPatent THERMAL BLANKET CIRCULATING AND CONTROL MEANS Edward MalcolmSmith, Mansfield, Ohio, assignor to Jet-Heat, Inc., Englewood, N.-J'., acorporation of New York Application January 9, 1957, Serial No. 633,293

16 Claims. (Cl. 219-39) This invention relates to improved thermalblankets of the type wherein a heat transfer fluid is circulatedtherethrough, and, more particularly, to improved apparatus forcirculating the fluid and automatically controlling the fluidtemperature to control the temperature of the blanket as desired.

Among the many advantages of the improved circulating and controlapparatus of the present invention are those resulting from the reducedsize, weight, and expense of the fluid circulator and the highlyeffective control action of the temperature control apparatus. Thisimproved circulator and control apparatus of the present invention isdescribed herein as being used for keeping the user comfortably warm,and many advantages are provided in this use.

The improved temperature control apparatus is extremely effective inmaintaining the desired temperature beneath the blanket adjacent to theusers body. Manual adjustment may conveniently be made to set thistemperature as desired. This improved apparatus continuously andautomatically controls the temperature of the circulating fluid inresponse jointly to two important factors. It automatically responds toboth of the following: (1) the amount of heat transfer from the fluidoccurring in the blanket and (2) the ambient temperature of the air inthe room. Furthermore, this improved control quickly responds in casethe fluid begins to overheat and immediately shuts ofif the heater.

Electric blankets have not proven fully satisfactory in many casesbecause of the ever present hazard of fire and shock and because of thereluctance of many people to sleep under an electrical device. Manypeople who have tried to use electric blankets have found that theirsleep is troubled by a hesitanc'y to move or roll about naturally forfear of damaging the live wires within the blanket.

Occasionally during use an electric blanket will become bunched orfolded while still energized. This reduces the exposed area and causesthe rolled up portions of the blanket seriously to overheat. To reducethis hazard efforts have been made to utilize a large number ofthermostats widely dispersed throughout the blanket. The use of numerousthermostats makes the blanket heavy and unnaturally bulky as well asgreatly increasing the number of electrical connections and raising themanufacturing cost. These scattered thermostats. in electric blanketsoften tend to be considerably delayed in response to localizedoverheating due to bunching. The blanket material itself insulates thethermostats so that they. cannot quickly sense a rise in temperatureexcept when the hot spot happens to be adjacent to one of them. All ofthese problems are highly satisfactorily overcome by the presentinvention as will be explained in detail further below. I I

Another problem with electric blankets is the necessity for protectingthe heating elements and electrical connectors in the blanket so thatthey are unaffected by dry-cleaning or washing. Waterproofing has addedp 2,866,072 Patented Dec. 23, 1958 to the manufacturing cost and weightas particular care is required in treating the conductors and circuitelements.

Since the shortcomings of the electric blanket were not satisfactorilycorrected, it has been suggested that a blanket be provided with meansfor circulating a temperature regulated fluid through appropriatepassages or tubes therein. This prior liquid blanket overcame thevarious hazards and psychological barriers occurring in the use of theelectric blankets and it lends itself readily to repeated washings anddry cleanings without any special precautions required. This priorblanket system is described and claimed in copending application SerialNo. 309,416, filed beptember 13, I952, and assigned to the same assigneeas the present application. The present invention is in the nature of afurther improvement thereover.

Among the advantages of the present invention is the provision of motorand pump means for circulating liquid through the blanket which arequiet-running and vibration free as desired. This improved circulator isless expensive to manufacture than prior units and is more efficient andrugged in operation, having a high strength against being knocked out ofadjustment by any rough usage.

Among the many advantages of the improved circulator and controlapparatus of the present invention are those resulting from the factthat the temperature is controlled in response both to the ambienttemperature in the room and in response to the temperature of the liquidreturning from the blanket to the circulator. In efiect, this improvedcontrol provides a highly successful combination of measurements of heattransfer occurring in the blanket and of ambient conditions.

In order to maintain a comfortable temperature beneath a blanketadjacent to the users body throughout the night regardless oftemperatures changes in the room, the improved apparatus of the presentinvention automatically varies the temperature of the circulatingliquid. Thus, as the room becomes colder during the middle of the nightthe temperature of the liquid in the blanket is raised. This maintains acomfortable temperature beneath the blanket in spite of the colderconditions in the room.

When the room warms up, the temperature of the circulating fluidautomatically is lowered to maintaina comfortable temperature beneaththe blanket.

As will be understood in detail from the present specification,maintaining constant the temperature of the liquid returning to thecirculator does not maintain a comfortable temperature beneath theblanket adjacent to the users body. As the temperature of the roomfalls, an increasing fraction of the available blanket heat is lost intothe room as a result of convection, conduction and radiation losses fromthe blankets to the room. Much less of this blanket heat is thentransferred down into the area beneath the blanket where it is useful.Also, as the room grows colder, more and more body heat is lost from theusers head and from the hands and arms if they are exposed. As the roomtemperature rises, these effects are, of course, reversed.

As a result of all of these operative relationships, as explained in thespecification, changes in the ambient temperature are a very importantfactor in obtaining proper temperature at the users body.

In the illustrative embodiment of the present invention a thermostat isadvantageously arranged to have a predetermined indirect sensitivity tothe temperature of the liquid returning from the blanket and has apredetermined direct sensitivity to the ambient conditions in the roomand responds thereto. Advantageously, this thermostat quickly respondsto any abnormal increases in the temperature of the liquid in thecirculator, thus immediately shutting off the heater to preventoverheatmg.

Accordingly, it is among the objects of the present invention to providea new and improved pump and heating unit and a sensitive and highlyeffective automatic control and combined overheating protector for aliquid thermal blanket. The illustrative embodiment of the presentinvention 1ncludes a unique arrangement wherein pump friction losses areso reduced that a low power electric motor is sufficient effectively tocirculate the fluid through the blanket tubes. Advantageously, thisimproved circulator pump is practically vibration free.

It is still another object of the present invention to provide a fluidheating chamber that is inexpensive to manufacture.

It is still a further object of this invention to provide a unique heatsensing control arrangement which is responsive to ambient temperatureand to the temperature of the liquid and of the storage tank and heater.

It is still another object of this invention to provide an easilyassembled circulating pump unit which may be manufactured at a minimumof cost.

Although in the accompanying drawings a preferred embodiment of thepresent invention is shown and is described in detail in thisspecification, it is to be understood that this embodiment is notintended to be either exhaustive or limiting of the invention, but, onthe contrary, is chosen for the purpose of illustrating the invention inorder that others skilled in the art may so fully understand theinvention, its principles and the application thereof, that they mayembody it and adapt it in numerous forms, each as may be best suited tothe requirements of its particular use.

In the drawings:

Figure l is a perspective view of a liquid thermal blanket cooperativelyconnected to the im r ved circulating and control apparatus of thepresent invention;

Figure 2 is a longi udinal sectional view of the improved circulatingand control a paratus;

Figure 3 is a horizontal sectional view of the circulating unit shown inFi ure 2, the view being taken genera long line 3-3 in Figure 2;

Figure 4 is a sectional end view of the circulating and controlapparatus. the view being taken generally along the line 4-4- of Figure2;

Figure 5 is a nlan view of the heat sensing c ntrol of the circul tor. tis view being taken along the line 5-5 in Figures 2 and 3;

Fi ure 6 is a schematic diagram of the electric circuit in thecirculating and control apparatus of the present invention;

Figure 7 is a plan View of the thermostat portion of the c ntr lapparatus; illustrating an alternative embodiment; and

Figures 8 and 9 are section views of the thermostat shown in Figure 7,taken on the lines 8-8 and 9-9, res ectively, in Figure 7.

Referring to Figure 1. a thermal blanket 10 of the circulating heattransfer liquid type is shown in cooperative arrangement with the imroved circulating, heating, and automatic temperature control apparatus12. The control apparatus 12 is provided with suitable means 11 forconnection to a conventional electrical outlet 13. The blanket isconnected to the improved apparatus 12 by means of a liquid return line14 and a supply line 16.

The thermal blanket It) has a grid of heat exchange passages shown asbeing formed by a series of flexible small diameter tubes of a plasticmaterial as described in the above copending application. A suitableheat transfer liquid is circulated through these tubes for warming (orif desired for cooling) e l The heat exchange passages include a pair ofheaders 18 and 20 at the foot of the blanket 10. A Se of h p tubes 22are connected from one of the headers 18 which serves as the intakeheader to the other or outlet header 20. The liquid is pumped by thecirculator apparatus 12 through the intake header 18 and itscommunicating heat exchange tubes 22 and circulated back to the outletheader Ztl. From the outlet header the liquid flows into the return line14 and then back into the circulator 12.

In Figures 2, 3 and 4 are illustrated a preferred embodiment of theimproved circulator of the present in vention. A protective casing 24protects the operating portion of the circulator, heating and controlapparatus 12. Appropriate openings in the casing 24 (as shown at thelower right in Figure 2) accommodate the entry of the supply and returnlines 16 and 14, and means 96 are provided at the opposite end of thecasing for air flow into the interior in order to sense the ambienttemperature.

The liquid for the system is introduced into a tank or reservoir 26through an opening 28 in its top surface 30. The side wall 32 and thetop portion 3% of the tank are preferably formed as an integral piece,cast from a suitable metal of high heat conductivity and corrosionresistance, such as cast aluminum, for example. In order to warm theheat transfer liquid, a heating element 34 is advantageously cast inplace integral with the side wall 32. A low power motor 36 of theshaded-pole type suitable for cooling by ambient air is mounted belowthe tank 26. The rotor 33 is of the squirrel cage type and is separatedfrom the stator magnet structure 4t by a thin air gap. A winding 42energizes the motor.

In order to seal the bottom of the reservoir 26, a housing 44 ofnon-magnetic material of relatively low electrical conductivity in theform of a cup is inserted into the air gap so as to surround the sidesand bottom of the rotor 38. This seal cup may advantageously be formedof stainless steel. A pump housing 46 extends out from the top of therotor seal cup and is preferably integral therewith. The pump housing 46may be made of magnetic or non-magnetic material as desired, but a morerigid and economical structure is provided by manufacturing the pumphousing and cup seal as one piece, in which case non-magnetic materialwould be used. A flange extends out from the top edge of the pumphousing and is secured to the tank body 32 by suitable means such as themachine screws shown. To insure a tight fit, a gasket 48 is placed abovethis flange at the area of contact.

An annular partition 50 is placed between the reservoir 26 and the pumphousing 46, being set into a shoulder recess 52. This partition 50 isprovided with a pump intake opening 53 at its center, thereby permittingliquid to flow down from the reservoir 26 into a pump chamber 54. Inorder to prevent the liquid being drawn down through the intake 53 fromswirling and developing a vortex which might cause air to be sucked intothe pump chamber, a cylindrical anti-swirl screen 55 surrounds the pumpintake. The partition 50 is firmly held in place by this anti-swirlscreen which is set into a recess 56 in the top portion of the tank body32 and presses down against the partition.

As shown most clearly in Figure 3, the pump chamber wall 46 ispreferably circular. A tangential outlet 58 feeds out from the perimeterof the pump chamber 54 and is connected to the supply line 16.

An impeller 60 consisting of two L-shaped blades 62 is positioned in thepump chamber 54 between the rotor 38 and the partition 50. The blades 62extend out into the upper portion of the chamber 54 near its perimeter,and are integrally secured to an impeller disk 64 which is provided witha central hole 66. The impeller disk is held down on top of the rotor bymeans of a flanged bearing bushing 68 which is press fitted down throughthe disk and down through the center of the rotor 38. A shoulder 70formed by a small flange on the upper end of the bushing presses thedisk 64 tightly into engagement mam with therefor 38. A fixed rotormounting shaft 72' passes up through the bushing 68, providing a postabout which the rotor 38 freely rotates. A thrust bearing shoulder 74preferably is formed as an integral part of shaft 72, and is positionedbetween the lower end of the bushing 68 and the bottom of the rotor cup44. To retain the rotatable bushing 68 on the post 72, a washer is helddown against a shoulder on the post by a nut screwe onto the reducedupper end of the post.

To operate the circulator, a liquid of moderate to high specific heatand relatively low viscosity, such as water containing a quantity of apermanent anti-freeze such as ethylene glycol, is poured into the tank26 through the opening 28 which is normally closed by a screw plug 78.The fluid flows from the tank, through the opening 53 and into the pumpchamber 54. The impeller 68 forces the liquid out of the pump chamberthrough the tangential outlet 58. During operation, a small amount offluid seeps down through the small clearance 82 between the rotor 38 andthe close fitting wall of the rotor cup housing 44. The seepage pathpasses down the clearance space 82 and into the space between the rotorand the bottom of the cup 44. The pressure at the center of the pumpchamber 54 is less than that near the perimeter. Due to this pressuredifferential, the seepage is forced up through the bushing 68 and aroundthe rotor shaft 72, and back into the pump chamber 54, thus desirablylubricating this bushing which is adapted to be lubricated in thismanner.

The movement of the seeping liquid around the rotor 38 and up along therotor shaft 72 also advantageously creates a lifting and centeringeffect. As a result, the tendency for Wear on the bearing surfaces ofthe rotor shaft 72 and the bushing 68 is greatly reduced. The centeringeffect also reduces the vibration of the rotating rotor and impeller,thereby keeping the running noise to a minimum as well as increasing theefficiency of the circulator. The power to operate the electric drivingmotor is reduced from a typical figure of about 35 watts required byformer circulator motors to about watts required by this embodiment. Asa result, the problem of motor cooling is substantially eliminated, asthe very small amount of input energy not utilized to drive the motorand pump readily dissipates to ambient through the casing 24. Withcirculation entirely shut oif and the motor operating continuously(without any input to the heater 34), tests have shown that the motorwill not overheat.

In addition to the features already referred to, it will also beobserved that the centrifugal circulator of the present invention hasthe advantage over a positive displacement pump that it is not adverselyaffected by any restrictions. thatmay occur in the circulation system; Apositive displacement pump, by comparison, may develop abnormally highpressures in the system upon occurrence of a restriction and can beseriously overloaded or even stalled. Furthermore, the centrifugal pumpis much less liable to develop vibration and noise which would requireauxiliary damping.

The fluid is circulated through the blanket as described above inconnection with Figure 1 and returns to the tank 26 through the returnline 14. The return line is connected up into the bottom of the tank 26by an inlet nipple '84 secured into the flange 47. Advantageously,

this return flow discharges'beneath the liquid level in the reservoir,thus providing an air seal and preventing entry or air into the returnline. Moreover, this construction has the advantage that both thetangential outlet 58 and the inlet nipple 84 are located in'the integralpump housing 46 and flange 47, rather than in the tank body 32. Thisenables the tank body 32'to be formed in one piece with the heatingelement 34 of a castable material, which does not lend itself'readily tomaking tubing connections by soldering; bracing or the like. Thisalsoeliminates the expense: of separately affixing heating means to the tankbody 32 and provides better heat conductivity and control action andsafety as explained below.

A temperature control 98 senses the ambient. temperature, and,indirectly, the average temperature of the fluid returning from theblanket and is ready immediately to respond to any tendency to overheatand thus shut off the heating element. In response to the ambienttemperature, and in accordance with the heat transfer occurring in theblanket as measured by the average temperature of the liquid in thereservoir 26, the control regulates the temperature of the circulatedliquid so as to keep the blanket user comfortable. In addition thiscontrol 90 shuts off the heating element if the tank body should becomeoverheaded. A unique arrangement has been provided which accomplishesall of these functions and yet uses but a single thermostat.

As shown in Figures 2, 3, and 5, a thermostat 90 is positioned on athermostat mounting plate 92 in a thermostat compartment 93. Thismounting plate electrically insulates the thermostat control 90, andprovides a predetermined amount of heat insulation between thethermostat and the circulator and reservoir. The mounting plate 92 islocated within the circulator casing 24 and is. aflixed to the tank body32 by means of a screw 95 or the like. The mounting plate is separatedfrom the tank body 32 by a heat conduction metal backing plate 94. Thethermostat 90 is attached to the lower end of the mounting plate 92 soas to be isolated from the tank body 32 and near the inflow of airthrough the port 96, to make it truly responsive to ambient airtemperature. Air convection ports 96 in the casing side wall 97 permitthe ambient air to circulate in the vicinity of the thermostat 96, asdescribed more fully hereinafter. The heat conduction plate backing 94carries a controlled portion of the heat from the tank body 32 to theareas adjacent to the thermostat 90.

In this way, the thermostat 90 is directly responsive to the temperatureof the ambient air. It is also indirectly responsive to the averagetemperature of the liquid in the reservoir 26 as determined by thecontrolled amount of this heat which is conducted through the backingplate 94 and through the mounting plate 92. Thus, it can be seen thatany desired balance can be achieved between ambient temperature effectand reservoir temperature effect. For most purposes, it is preferable torely primarily on ambient temperature for control purposes and to sensereservoir temperature for protective purposes. If for any reason theheating element 34 tends to overheat, this heating is conducted throughthe heat conduction plate 94 to the thermostat. It will be appreciatedthat the position of the heat conduction plate closely adjacent to thebulge on the tank body containing the central part of the heatingelement renders the thermostat quickly responsive to overheating.

In order to obtain a desirable joint response to liquid temperature andambient temperature a conduction plate 94 of metal of good heatconductivity such as aluminum or copper of an inch thick and aninsulating plate of rigid insulating material /8 of an inch thick suchas phenol formaldehyde (Bakelite) or methyl methacrylate (Lucite orPlexiglas) may be used.

The thermostat 90 may comprise a bimetal strip 98 which is attached atone end to the mounting plate 92. At this end, the strip 98 is incontact with a wiring terminal 99.

At its free end, the strip 98 carries a contact button 1%. which isengageable with a similar button 102 mounted on the plate 92 andincluded in the electric circuit described hereinafter. The fixedcontact button 102 preferably is mounted on a small permanentmagnet'elecut 104 which cooperates with the movable bimetal strip 98 toensure positive action in opening and closing of the contacts. The fixedcontact 102 is connected electrically to a wiring terminal 103.

Near its mounted end, the bimetal strip 98 carries an L-shaped levermember 105 which is engageable by a rotatable cam 106 above the strip 90for adjusting the temperature at which the contacts 100, 102 will openand close. The cam 106 is carried at the lower end of an adjusting shaft107 of electrical and thermal insulation material which is heldrotatably in a half-round vertical groove in the mounting plate 92 bysuitable means such as a spring clip 108. The shaft 107 extends upwardlythrough the casing 24. At its upper end outside the easing, the shaftcarries a control knob 109 to permit ready adjustment of the thermostat.In the usual case, the control knob will be calibrated to referenceindicia (not shown) on the top of the casing 24.

The thermostat 91B is connected in the electrical circuit of the controlunit 12 as shown in Figure 6. In this circuit, the thermostat 91) isconnected in series with the heater 34 across the motor winding 42. Inthis circuit, it will be observed that the bimetal strip 98 is shown asa resistance element. This strip preferably is made of a combination ofrelatively high resistance materials, such as chrome-nickel steels, sothat current flow therethrough will result in some heating of thebimetal strip. This heating of the strip 98 serves two purposes. For onething, it provides a small amount of heat in the thermostat compartment93 which creates a chimney effect, inducing ambient air flow through thecompartment 93. As the sensing element 98 is located in the lower partof the chamber 93, it is seen that this element will be exposed to freshincoming ambient air, to be responsive thereto. The control circuit alsopreferably includes a manual on-olf switch 111 which may be locatedadjacent to the control knob 109 (Figure 2).

When the on-off switch 111 is closed, the motor 36 will operatecontinuously to maintain constant circulation of liquid through theblanket 10. When the unit is first turned on, it can be. assumed thatthe thermostat contacts 100, 102 will be closed so that electric currentalso will start to flow through the heater 34- and the thermostat 90.This will initiate heating of the liquid in the reservoir 26 and alsowill start heating the bimetal strip 98 to induce air circulationthrough the thermostat chamber 93.

Current flow through the heater 34 and the thermostat 90 will continuefor a period of time determined by the temperature of the ambient air towhich the strip 98 is exposed. Also, the temperature of the circulatingliquid entering the reservoir 26 will influence the temperature of thechamber wall In turn, this will have a hearing on the temperature of theconducting plate 94 and of the lower portion of the mounting plate 92.

Thus, the bimetal strip will be exposed to three temperature efiects;one being due to current flow through the strip 98, another being thetemperature of the ambient air entering the chamber 93, and the thirdbeing the return liquid temperature. After a period of current flowthrough the heater 34 and thermostat 90, the strip 98 will become heatedsufficiently to open the thermostat contacts 1130, 102 and shut off theheating current.

After a short time, assuming no change in ambient temperature andassuming that the liquid temperature still is not up to the requiredlevel, the thermostat contacts will close again and flow of heatingcurrent will resume. This on-oii' cycling will continue as long as theunit continues in operation, with variations in cycle time as determinedby ambient temperature and liquid temperature.

The current tiow through the bimetal strip 93, and the consequentheating effect thereof on the strip will be essentially constant.Therefore, the time required for the thermostat strip 98 to open thecontacts 100, 10.; on each cycle will depend on the rate of heat lossfrom the strip. In turn, this will depend on the temperature differencebetween the ambient air and the strip 93, and also the temperaturedifference between the mounting plate 92 and the strip. An increase ineither the ambient air temperature or the mounting plate temperaturewill reduce the heater on time and increase the heater off time, therebyreducing the average heat input to the circulating liquid to permit thetemperature thereof to decrease. As far as the mounting platetemperature is concerned, it is seen that this arrangement provides anelfective safety control.

If, for example, circulation through the blanket is interrupted for somereason, the temperature of the reservoir wall 32 will go up rapidly.This temperature rise will quickly be transferred to the lower portionof the mounting plate 92 by the backing plate 94, causing the strip 9%to bend and hold the contacts 100, 102 open until the chamber wall 32has cooled to a safe level.

In Figures 7-9 there is shown an alternative form of thermostat in thecontrol unit of the present invention. In this embodiment, thethermostat comprises a main bimetal strip 98 mounted at one end on aspacer block 113 and attached by rivets 114 or the like to the mountingplate 92. The rivets 114 extend through the plate 92 to engage a wiringterminal 99 on the rear side of the plate 92. Also, the wiring terminal103 for the fixed contact button 102 is located on the rear side of theplate 92.

In place of the backing plate 94 of Figures 2, 3 and 5, the controlthermostat 90 in Figures 7-9 further includes a supplementary bimetalstrip on the back side of the mounting plate 92. At one end, thissupplementary bimetal strip 115 is attached to the mounting plate 92 byany suitable mounting means and so located as to engage the reservoirwall 32 when the mounting plate is in position. Accordingly, it is seenthat the supplementary strip 115 is in direct thermal contact with thechamber wall 32 and will be directly responsive to the temperaturethereof.

The supplementary strip 115 extends to a point adjacent to the mainbimetal 98, and the free end of the strip 115 is engageable with one endof a reciprocable plunger 116 of insulating material. This plunger 116extends through the mounting plate 92 so that its other end isengageable with the main bimetal 98 adjacent to the contact button 100.The plunger 116 is slidable endwise through the panel 92, so that it canbe moved by the supplementary strip 115 into engagement with the mainbimetal 98, upon flexing of the strip 115.

With this arrangement, it is preferable to have the control ofcirculating liquid temperature primarily dependent on the main bimetal98, with the supplementary strip 115 being primarily operative as asafety control. In other words, the main bimetal 98 will cycle theheater on and off at a rate determined by the'ambient temperature, whilethe supplementary strip 115 will function at temperatures above thedesired level to force the main strip into open contact position throughthe medium of the reciprocable plunger 116.

It will be understood, of course, that the desired operating temperaturecan be selected by rotating the knob 109, as previously described, thata change in the setting of the knob 109 will alter the temperature atwhich the main bimetal contacts 100, 102 will open and close. It will beobserved that any change in the setting of the .control knob 109 willalso change the temperature at which the supplementary strip 115 acts onthe main bimetal 98 to open the contacts 100, 102.

With the arrangement shown in Figures 7-9, the effect of this is thatwhen a lower liquid temperature is selected at the knob 109, thesupplementary bimetal 115 becomes effective at a higher temperature thanbefore, because of the greater curvature of the main bimetal 98. In manyinstances, it is preferable to have the response temperature of thesupplementary strip 98 increase and decrease in step with increases anddecreases in the temperature selected at the knob 109. This isaccomplished very readily by reversing the relative locations of theplunger 116 and the contacts 100, 102. In other words, if the plunger116 is so located as to contact the strip 98 at I or near the f ree endthereof, while the contacts 100, 102

are placed a slight distance inward from the free end of the strip, theresponse temperature of the supplementary strip will rise and fall asthe temperature selected at the knob 109 is raised and lowered. This, ofcourse, advantageously provides better protection against overheating,particularly when a relatively low liquid temperature is selected at theknob 109.

The circulator, heating and control apparatus is efiicient in operationrequiring'only a ten watt motor and is very quiet. Typical overalldimensions of the casing 24 are 3 inches high, 5% inches long, and 3%inches wide.

From the foregoing it will be understood that the improved circulating,heating and control apparatus of the present invention described aboveis well suited to provide the advantages set forth. It will beunderstood that many changes and modifications may be made of thevarious features of this invention and the apparatus described hereinmay be varied in various parts, all Without departing from the truespirit and scope of the invention as covered in the following claims.

What is claimed is:

1. Improved circulating and heating apparatus for use with thermalblankets comprising a tank, heating means integral with said tank, apump housing and impeller beneath said tank, said pump housing having anintake communicating with the interior of said tank through the lowerportion of said tank, said pump housing having an outlet adapted to becoupled to a thermal blanket, and an electric motor drive meansconnected to said impeller.

2. Improved circulating and heating apparatus for use with thermalblankets comprising a tank, heating means integral with said tank, apump housing and impeller beneath said tank, said pump housing formingat least a portion of the bottom of said tank and having an intakecommunicating with the interior of said tank, said pump housing havingan outlet adapted to be coupled to a thermal blanket, an electric motordrive means connected to said impeller,

3. Improved circulating and heating apparatus for use with thermalblankets comprising a tank having top and side portions, a bottom forsaid tank including an impeller chamber integral therewith, saidimpeller chamber having an intake communicating with the liquid in thebottom of said tank, said impeller chamber having an outlet adapted tobe coupled to a thermal blanket, an electric motor drive means connectedto said impeller, and heating means for warming the liquid in said tank.

4. Improved circulating and heating apparatus for use with thermalblankets comprising a tank body, heating means for warming liquid insaid tank, an integral member secured to said tank body and forming thebottom of said tank, said member having a cup therein extendingdownwardly and said member defining an impeller housing above said cupand beneath said tank, said impeller housing having an impeller thereinand communicating with the interior of said tank at the bottom of saidtank, said impeller housing having an outlet adapted to be coupled to athermal blanket, and electric rotor drive means within said cupconnected to said impeller.

5. Improved circulating and heating apparatus for use with thermalblankets comprising a tank having a body portion, an electricalresistance heating element integral with said body portion, an integralmember sealing up the bottom of said tank, said member having a deepcylindrical cup therein and said member defining an impeller housingabove said cup and beneath said tank body portion, said impeller housingcommunicating with the liquid in the lower portion of said tank body, anelectric rotor within said cup, an impeller secured to said rotor andbeing positioned in said im eller housing beneath said tank bodyportion, an outlet from said impeller housing adapted to be secured tosaid blanket, and an electric motor magnet structure around s id cup.

6. Improved circulating and heating apparatus of the type: a.circulating liquid through a liquid thermal means whereby liquid flowsfrom said tank down into said pump means by gravity flow, said pumpmeans having an outletadapted to be coupled to a thermal blanket,

' and a liquid return from said thermal blanket entering said tankbeneath the liquid level therein, thereby forming an air seal.

7. Improved circulating and heating apparatus of the type forcirculating liquid through a liquid thermal blanket, said apparatuscomprising a tank, heating means integral with said tank, a pumpimpeller beneath said tank, electric motor drive means including a rotorconnected to said impeller, and a housing enclosing said impeller andthe rotor of said electric motor, said housing eifectively scaling up aportion of the bottom of said tank.

8. Improved circulating and heating apparatus of the type forcirculating liquid through a liquid thermal blanket, said apparatuscomprising a tank, heating means integral with said tank, a pumpimpeller beneath said tank, electric motor drive means including astator and a rotor connected to said impeller, and a housing enclosingsaid impeller and the rotor of said electric motor, said housing beingplaced in the air gap between the rotor and the stator of said electricmotor.

9. Improved circulating and heating apparatus of the type forcirculating liquid through a liquid thermal blanket, said apparatuscomprising a tank, heating means arranged to warm liquid in said tank, apump impeller of the centrifugal type beneath said tank, electric motordrive means including a rotor beneath said impeller connectedto' saidimpeller and a stator, a housing enclosing said impeller and the rotorof said electric motor, said I housing communicating with the interiorof said tank through an impeller intake opening over the center of saidimpeller, a tangential outlet from said housing near the periphery ofsaid impeller, and a vertical shaft within said housing extending upthrough the center of the rotor for mounting said rotor; the wall ofsaid housing being in closely spaced relationship with said rotor anddefining a small gap, whereby said impeller rotates as the rotor isrotated and seepage of some of the circulating liquid is forceddownwardly between the housing wall and the rotor and upwardly about theshaft at the center of the rotor, creating an uplift effect upon saidrotor.

10. Improved circulating heating and control apparatus of the type forcirculating a heat transfer liquid through a thermal blanket, saidapparatus controlling the temperature of the space beneath said blanketin accordance with changes in room temperature, said apparatuscompri:ing a casing, a liquid reservoir tank within said casing andhaving a body portion of metal of good heat conductivity, a resistanceheating element within the body of said tank, a pump and electric drivemeans within said casing, said pump having an intake communicating withsaid tank and an outlet adapted to be coupled to said blanket, a supportof good heat conductivity secured to said tank body, a heat insulatingmounting on said support, a thermostat on said mounting, and meansdefining an ambient air convection path through said casing, saidthermostat being responsive to the air in said path and to the heatconducted through said support and mounting.

11. Improved circulating, heating and control apparatus as claimed inclaim 10 and wherein said thermostat is secured to said support at adistance from the connection of said support to said tank body, andsaidthermostat is positioned in said air convection path near the pointwhere the air enters said casing, thereby to sense ambient airtemperature.

12. Improved circulating and heating apparatus for use with thermalblankets comprising a tank having a body portion with integral side andtop walls, heating means integral with said side and top walls, anelectric motor having a stator and a rotor, said rotor being beneathsaid tank, a cup-shaped liquid seal around said rotor within the gapbetween said rotor and stator, said seal defining an impeller housingabove said rotor and having a flange secured to said side walls, saidseal effectively forming the bottom of said tank, said impeller housinghaving an annular partition forming the top of said housing, saidpartition having a central opening communicating with said tank andforming the intake for said impeller housing, an impeller within saidhousing and aiiixed to said rotor, an outlet from saidhousingcommunicating with said blanket, a thermostat, a support of good heatconductivity being secured to said side and top walls of the tank body,said thermostat being secured to said support at a distance from saidside and top Walls of the tank body, and heat insulating materialbetween said thermostat and the support, thereby to predetermine theresponse of said thermostat to the temperature within said tank, saidthermostat being exposed directly to the ambient air.

13. Improved circulating and heating apparatus as claimed in claim 12and including liquid return discharge means adapted to be coupled to thereturn line from said blanket, said return discharge means being securedto said flange and discharging into the bottom of said tank, thereby tobe beneath the liquid level in said tank.

14. Improved circulating and heating apparatus as claimed in claim 12and wherein said tank includes a cylindrical anti-swirl screen therein,a recess in said top wall of the tank receiving the upper end of saidscreen, the lower end of said screen pressing down upon said portionaround said pump intake opening.

15. Improved circulating and heating apparatus of the type forcirculating heat transfer liquid through a liquid thermal blanket, saidapparatus comprising: a casing, a liquid reservoir in said casing, meansin said casing adapted to heat the liquid within said reservoir, meansin said casing for circulating liquid through said reservoir, anelectrical control circuit connected to said heating means,

a thermostat for said control circuit including a bimetal strip, a firstfixed contact in said control circuit, a second movable contact in saidcontrol circuit carried by said bimetal strip and engageable with saidfirst contact, said strip being movable upon heating thereof to opensaid contacts and de-energize said heating means, a second bimetal stripdirectly contacting a wall of said reservoir, and means coupling saidstrips and operable to move said first strip in a contact-openingdirection upon heating of said second strip.

16. Improved circulating and heating apparatus of the type forcirculating heat transfer liquid through a liquid thermal blanket, saidapparatus comprising: a casing, a liquid reservoir in said casing, meansin said casing adapted to heat the liquid within said reservoir, meansin said casing for circulating liquid through said reservoir, an

electrical control circuit connected to said heating means, 1

a thermostat for said control circuit including a bimetal strip, a firstfixed contact in said control circuit, a second movable contact in saidcontrol circuit carried by said bimetal strip and engageable with saidfirst contact, said strip being movable upon heating thereof to opensaid contacts and de-energize said heating means, means defining anambient air convection path through said casing, said bimetal stripbeing located in said air convection path, said bimetal strip beingincluded in said electrical control circuit to constitute a portion ofthe path for current flow to said heating means, said bimetal stripcomprising a combination of materials of relatively high electricalresistance whereby to provide heating of said strip in response toelectric current flow therethrough, thereby to effect cyclical operationof said heating means.

References Cited in the file of this patent UNITED STATES PATENTS1,896,953 Hassell Feb. 7, 1933 2,312,353 Miller Mar. 2, 1943 2,319,730Garraway May 18, 1943 2,753,435 Jepson July 3, 1956

